Radiation polymerizable vinyl ester resins containing 2-oxazoline and guanidine additives

ABSTRACT

THE ADDITION OF AT LEAST ABOUT 0.3 WEIGHT PERCENT OF A 2-OXAZOLINE, A GUANIDINE OR CERTAIN AMINES TO A THERMOSETTABLE MIXTURE OF A NONVOLATILE VINYL MONOMER AND A POLYMERIZABLE VINYL ESTER RESIN REDUCES THE DOSAGE LEVEL OF IONIZING RADIATION REQUIRED TO CURE THE MIXTURE.

United States Patent Office 3,810,826 Patented May 14, 1974 3,810,826RADIATION POLYMERIZABLE VINYL ESTER RESINS CONTAINING 2 OXAZOLINE ANDGUANIDINE ADDITIVES Inder Mani, Midland, Mich., assignor to The DowChemical Company, Midland, Mich. No Drawing. Filed May 13, 1971, Ser.No. 143,268 Int. Cl. C08d 1/00; C08f 1/00 US. Cl. 204-15915 11 ClaimsABSTRACT OF THE DISCLOSURE The addition of at least about 0.3 weightpercent of a 2-oxazoline, a guanidine or certain amines to athermosettable mixture of a nonvolatile vinyl monomer and apolymerizable vinyl ester resin reduces the dosage level of ionizingradiation required to cure the mixture.

BACKGROUND OF THE INVENTION This invention relates to the field ofionizing radiation cure of polymerizable materials and to coatings ofsame and especially relates to a promoter to reduce the ionizingradiation level or dosage necessary to eifect a cure of said materials.

From a commercial standpoint radiation curing offers a number ofadvantages over thermal catalyst-initiated cures: immediate initiationof polymerization, extended pot-life of the curable materials, littletemperature rise so heat sensitive substrates may be employed incoatings, better control of the polymerization reaction, superiorsubstrate-coating bonds are produced and much higher concentration ofradicals may be produced instantaneously. However, these advantages arediflicult to realize if the curable materials require high curing dosesof ionizing radiation since the economics become prohibitive. Commercialization then depends on reducing the cost of the curing processby finding methods and materials to effect a cure at lower dosages.

The search for means to accelerate or promote radiation curing isevident by a number of patents relating to certain polymerizablematerials. While neither the promoters or the polymerizable materialsemployed correspond in any way to this invention, patents representativeof such eiforts include US. 3,202,513; 3,251,759; 3,265,- 604; 3,352,771and 2,979,446. Commercially it is desirable to be able to cure atdosages of no more than 2 to 3 megarads but it would be of greatadvantage to be able to cure at 1 megarad and preferably even less.

SUMMARY OF THE INVENTION According to this invention the curing dosageof ionizing radiation required to cure in an inert atmosphere a mixtureof a nonvolatile vinyl monomer and a polymerizable vinyl ester resin isreduced by adding to the mixture at least 0.3 weight percent of certainnitrogen containing materials.

The vinyl ester resin is prepared by reacting about equivalent amountsof a dicarboxylic acid half ester having the formula where R, ishydrogen or an alkyl group of 1 to 4 carbons, R is an alkylene group of2 to 6 carbons and R is phenylene, cyclohexylene, alkylene or anunsaturated bivalent hydrocarbon radical, with a polyepoxide of apolyhydric phenol having more than one epoxide group per molecule. Thenitrogen materials include various 2-oxazolines, guanidines and certainamines which are more fully described hereafter.

DESCRIPTION OF THE INVENTION The general methods by which vinyl esterresins may be prepared are thoroughly described in the patentliterature. Representative patents which describe the resins and theirpreparation include US. 3,066,112; US. 3,179,623; US. 3,256,226; US.3,301,743 and US. 3,377,406.

In particular the vinyl ester resins employed in this invention aredescribed in US. 3,3 67,992 along with methods for their preparation.More particularly this invention relates to said resins prepared frompolyepoxides of polyhydric phenols having more than one epoxide groupper molecule.

The vinyl ester resins are prepared by reaction of essentiallyequivalent amounts of said polyepoxide of a polyhydric phenol and adicarboxylic acid half ester having the formula where R is hydrogen oran alkyl group of l to 4 carbons, R is an alkylene group of 2 to 6carbons and R is phenylene, cyclohexylene, alkylene or an unsaturatedbivalent hydrocarbon radical.

Said half esters are conveniently prepared by esterification of ahydroxyalkyl acrylate or methacrylate with an equal molar amount of adicarboxylic acid, or preferably a dicarboxylic acid anhydride where itexists. For example, equal molar amounts of Z-hydroxyethyl acrylate andmaleic anhydride may be reacted to form said half ester. Accordingly Rin the formula is usually hydrogen or methyl. In place of 2-hydroxyethylacrylate one may employ hydroxypropyl or hydroxybutyl acrylate ormethacrylate. Also, in place of maleic anhydride or maleic acid one mayemploy fumaric acid, itaconic acid, citraconic acid, adipic acid, theisomeric phthalic acids and the like. The anhydrides of said acids,where available, may also be used.

Said half ester is reacted with a polyepoxide of a polyhydric phenolwherein the polyepoxide has an epoxide equivalent weight of about up to1000 and even higher. Said polyepoxides are made by reacting at leastabout two moles of an epihalohydrin, such as epichlorohydrin, with onemole of a polyhydric phenol and a sufiicient amount of an alkali tocombine with the halogen of the halohydrin. Polyhydric phenols includethe familiar bisphenol A as well as p,p-dihydroxydiphenyl,p,p,-dihydroxyphenyl sulfone, p,p,'-dihydroxybenzophenone, p,p,'-dihydroxydisphenylmethane, the various other position isomers of theabove polyhydric phenols, polyhydric phenolic formaldehyde condensationproducts (novolak resins) and the like. Mononuclear phenols such asresorcinol, catechol, hydroquinone, phloroglucinol and the like may alsobe employed. The polyepoxides are characterized in having more than oneepoxide group per molecule.

Various catalysts may be used in the preparation of vinyl ester resins.Catalysts include tertiary amines such astris(dirnethylaminomethyl)ph-enol, onium catalysts, triphenyl stibineand triphenyl phosphine and the like. Usually hydroquinone or other likepolymerization inhibitors are added to prevent polymerization during thpreparation of the resin.

According to this invention the polymeriza ble materials comprise amixture of said vinyl ester resin with a copolymerizable vinyl monomerwhich is nonvolatile. By nonvolatile it is meant to exclude monomerswhich are predominantly gases at ambient temperatures. It is obviousthat if the monomer is too volatile a substantial portion of the monomerwould evaporate from a film or coating before the mixture of monomer andresin could be cured. Monomers which are normally liquid at roomtemperature may be used even though there may be a small loss of monomerby evaporation. It is possible to operate the process of this inventionunder higher pressures than atmospheric pressure to minimize any loss ofsaid normally liquid monomers.

Nonvolatile vinyl monomers which may be employed with this inventioninclude both monoand polyunsaturated monomers. Polymerizablemono-unsaturated monomers include alkenyl aromatic monomers such asstyrene, vinyl toluene, chlorostyrenes and the like; vinyl carboxylicacids such as acrylic and methacrylic acid; vinyl nitriles such asacrylonitrile and methacrylonitrile; alkyl and hydroxyal'kyl esters ofvinyl carboxylic acids, wherein the alkyl groups contains from 1 to 8carbons, such as methyl acrylate, butyl acrylate, methyl ester ofcinnamic acid, cyclohexyl methacrylate, hydroxyethyl methacrylate,hydroxypropyl acrylate, hydroxybutyl acrylate and the like; vinyl amidemonomers such as acrylamide, diacetone acrylamide and the like; ormixtures thereof.

A variety of polyunsaturated polymerizable monomers within the aboveclasses may be used including ethylene glycol dimethacrylate,trimethylol propane trimethacrylate, methylene bisacrylamide and othersimilar monomers.

The polymerizable materials of this invention are especially useful incoating various substrates such as metal, wood and the like either as aprimer coating and/ or a finished coating. In order to obtain thebenefits of this invention at least 0.3 weight percent of the nitrogencontaining material is added to the polymerizable materials. While quitelarge amounts of the nitrogen containing material may be added there isno advantage in doing so. Preferably the amount ranges from about 0.5 to10 weight percent and most preferably from about 1.5 to weight percent.

When employed as coating formulations other additives may beincorporated into the coating, for example, various inert fillers andpigments such as kaolin clay, titanium dioxide, silica, variousinorganic oxides and the like. Films cast from the coating formulationsmay be rapidly cured by exposing them in an inert atmosphere to ionizingradiation (accelerated particulate radiation). A beam intensity of atleast 50 microamperes is usually employed, but this invention is notlimited thereto and lower beam intensities may be employed. Generallythe films or coatings will range in thickness from about 0.1 mill up toabout mils. However, depending on the accelerating voltage, thicknessesup to 250 mils or higher are feasible. The radiation curing step shouldbe performed in an inert atmosphere. By this it is meant an atmospherewhich is essentially free of oxygen since the presence of oxygen mayresult in an undesirable tacky surface. It is sufiicient for thispurpose to place a thin film of a plastic material such as a polyester(Mylar) film on the cast film or coating. Other means may be used suchas curing in a chamber containing an essentially oxygen free atmospheresuch as nitrogen, helium, argon and the like.

Accelerated particulate (ionizing) radiation includes particles such aselectrons, protons, deuterons, other ions and the like. However, from anindustrial standpoint, the cost and availability of machines limitionizing radiation curing to accelerated electrons for the immediatefuture. A variety of devices are available to provide acceleratedelectron radiation or varying voltages and beam intensities. Typical ofsuch devices is the familiar Van de Graaf accelerator. Similarcommercial accelerators utilizing various acceleration means areavailable from Texas Nuclear Corporation, (cascade rectified system),High Voltage Engineering, (insulated core transformer system), GeneralElectric (a resonant transformer design) and Radiation Dynamics, Inc.(radio frequency cascade rectifier system).

Nitrogen containing materials include 2-oxazolines, guanidines andcertain amines. Typical of the 2-oxazolines are 2-oxazoline itself, andsubstituted 2-oxazolines having the formula wherein R' and R" may behydrogen, methyl, ethyl, phenyl and the like. R may be an alkyl, aryl,aralkyl group or H. Such substituted oxazolines include Z-methyl-2-oxazoline, 2,5-diphenyl-Z-oxazoline; 2-phenyl, S-methyl-2-oxazolidine;Z-methyl, 5-phenyl-2-oxazoline and the like. Also included within theterm 2-oxazolines are the his oxazolines such as 2,2'-tetramethylenebis(2-oxazoline), 2,2. oxydiethylene bis(2 oxazoline);2,Z'-thiodiethylene bis(2-oxazoline) and the like. Guanidines includeguanidine, tetramethyl guanidine and the like.

Amines which may be employed have the formula R R R N wherein R may bean alkyl or an aralkyl group, R and R each may be hydrogen or an alkylgroup or R and R together may be a cyclic alkylene radical or anoxydialkylene radical. Alkyl groups include methyl, ethyl propyl,n-butyl, isobutyl and higher alkyl groups. Typical amines include mono-,diand tri-n-butyl amine, di-isobutyl amine, triethyl amine,cyclohexylamine, benzyl amine, morpholine, piperidine and the like.

The following non-limiting examples will further illustrate theinvention. All parts and percentages are by weight unless otherwisespecified.

EXAMPLE 1 A vinyl ester resin was prepared by reacting 2-hydroxyethylacrylate (30.5%) with maleic anhydride (25%) to form a half ester whichwas subsequently reacted with a glycidyl polyether of bisphenol A havingan epoxide equivalent weight (EEW) of 186-192 (D.E.R. 331) according tothe procedure of US. 3,367,992. The resin was then mixed with a monomerin the weight proportion of 2/1 respectively. The monomer of resin A-lwas n-butyl acrylate and the monomer of resin B-l was styrene. Themonomer of resin C-l was Cellosolve acrylate (60/40). To these mixtureswas added 3% of various nitrogen containing compounds.

A film was cast from each of the resin mixtures with a 7 mil draw-downbar on a Q-panel (4" x 12" x .03) and covered with a 2 mil sheet ofMylar (polyester) film to exclude air. The coated polished steel Q panelwas then passed through a 2 mev. electron beam from a Van de Graafaccelertaor filtered with 0.33 gm./cm. A]. A 50 microampere beam currentand a conveyor speed of 3.4 cm./sec. delivered a dose of 0.1 megarad(mrad) for each pass through the beam.

The curing dose in megarads (mrad) for each of the coated panels isshown below.

When the resin of the previous example was mixed with 2-hydroxyethylacrylate (1/1), the mixture required 0.4 mrad to cure. The addition of3% of dibutyl amine reduced the curing dose to 0.15 mrad.

EXAMPLE 3 Using resin A-l the dosage to cure was determined with varyingamounts of di-n-butyl amine according to the procedure of Example 1.

The tests showed at least about 0.3% is necessary. A minimum is found inthe range of about 1.5 to 5% and no advantage is found above aboutEXAMPLE 4 A vinyl ester resin was prepared by reacting 2-hydroxyethylacrylate (25.55%) with phthalic anhydride (32.6%) to form a half ester.The half ester Was then reacted with D.E.R. 331 (41.85%) to form thevinyl ester resin which was then mixed with a monomer in the proportionsof 2/ 1 as before. Resin A-4 contained n-butyl acrylate and resin B-4contained styrene. Films were cast and cured by the procedure of Example1.

Resin Nitrogen additive (3%) 11-4, mrad Nona di-n-Butyl amineTetramethyl guanidine. 2-oxazoline B-4, mrad Benzylamine2,2'-tetra.methylenebis(2-oxazohne) It will be understood that thepresent invention is not limited to the specific details described abovebut may embody various modifications insofar as they are defined in thefollowing claims.

What is claimed is:

1. A process for curing a mixture of a polymerizable vinyl ester resinand a nonvolatile vinyl monomer selected from the group consisting ofalkenyl aromatics, vinyl carboxylic acids, vinyl nitriles, vinyl amides,alkyl and hydroxyalkyl esters of vinyl carboxylic acids wherein thealkyl group contains from 1 to 8 carbons, and mixtures thereof, saidprocess comprises exposing said thermosettable mixture in an inertatmosphere to ionizing radiation in the presence of at least about 0.3weight percent based on the weight of the mixture of a nirogencontaining compound selected from the group consisting of 2-oxazolinesand guanidines; and wherein said vinyl ester resin is prepared byreacting about equivalent amounts of a polyepoxide of a polyhydricphenol having more than one epoxide group per molecule with adicarboxylic acid half ester having the formula where R is hydrogen oran alkyl group of 1 to 4 carbons, R is an alkylene group of 2 to 6carbons and R is phenylene, cyclohexylene, alkylene or an unsaturatedbivalent hydrocarbon radical.

2. The process of claim 1 wherein said nitrogen compound is present inabout 0.3 to 10 weight percent.

3. The process of claim 1 wherein said nitrogen compound is present inabout 1.5 to 5 weight percent.

4. The process of claim 1 wherein said nitrogen compound is guanidine ortetramethyl guanidine.

5. The process of claim 1 wherein said nitrogen compound has the formulawherein R and R" may be hydrogen, phenyl, ethyl or methyl and R may behydrogen, an alkyl group, an aryl group or an aralkyl group.

6. The process of claim 1 wherein said 2-oxazoline is2,2'-tetramethylene bis(Z-oxazoline), 2,2'-oxydiethylenebis(2-oxazoline) or 2,2'-thiodiethylene bis(2-oxazoline).

7. A thermosettable mixture suitable for curing by exposure to lowlevels of ionizing radiation comprising a mixture of a polymerizablevinyl ester resin and a nonvolatile monomer selected from the groupconsisting of alkenyl aromatics, vinyl carboxylic acids, vinyl nitriles,vinyl amides, alkyl and hydroxyalkyl esters of vinyl carboxylic acidswherein the alkyl group contains from 1 to 8 carbons, and mixturesthereof, said thermosettable mixture containing at least about 0.3weight percent based on the weight of the mixture of a nitrogencontaining compound selected from the group consisting of 2-oxazolinesand guanidines; and wherein said vinyl ester resin is prepared byreacting about equivalent amounts of a polyepoxide of a polyhydricphenol having more than one epoxide group per molecule with adicarboxylic acid half ester having the formula where R is hydrogen oran alkyl group of 1 to 4 carbons, R is an alkylene group of 2 to 6carbons and R is phenylene, cyclohexylene, alkylene or an unsaturatedbivalent hydrocarbon radical.

8. The composition of claim 7 wherein said nitrogen compound is presentin about 0.3 to 10 weight percent.

9. The composition of claim 7 wherein said nitrogen compound is presentin about 1.5 to 5 weight percent.

10. The composition of claim 7 wherein said nitrogen compound isguanidine or tetramethyl guanidine.

11. The composition of claim 7 wherein said nitrogen compound has theformula RHC-N R"H i l-R References Cited UNITED STATES PATENTS 3,632,8611/ 1972 Hargis 260-837 R 3,597,343 8/1971 Delzenne et al. 204-159233,552,986 1/1971 Bassemir et a1. 204-15923 3,558,387 1/1971 Bassemir etal. 204-15923 3,367,992 2/1968 Bearden 260-837 R 3,650,927 3/1972Levinos 204-15923 2,921,006 1/1960 Schmitz et al, 204-15915 3,660,2175/1972 Kehr et a1 204-15922 3,650,669 3/1972 Osborn 204-15922 2,673,1513/1954 Gerhart -7 MURRAY TILLMAN, Primary Examiner R. B. TURER,Assistant Examiner U .8. Cl. X.R.

117-9331, 132 B, 132 BB, 161 ZB, UZ; 204-45916, 159.22, 159.23; 260-41A, 41 B, 836, 837R

